Fluidized catalytic cracking (“FCC”) is a key process in modern petrochemical refineries due to the large volume of gasoline and distillate fuels that it generates. An integral part of FCC operation is the catalyst, which is particularly designed in view of a unit's product needs, feedstock and operating limitations. The health of the FCC catalyst is typically monitored by taking samples of the circulating catalyst (the so-called equilibrium catalysts) and performing tests to measure physical/chemical properties and the activity of the catalyst under standard laboratory testing. Normally, data from these measurements provides relevant information as to yield changes resulting from changes in the catalyst itself. These changes can include damage to the catalyst suffered as a result of high temperatures or the effects of metals contamination. Metals contamination has long been known to poison the catalytically active sites of the FCC catalyst as well as sometimes serving as catalysts of undesirable reactions themselves. For example, nickel deposited on the surface of an FCC catalyst itself acts as a catalyst to dehydrogenate FCC feedstocks, resulting in higher hydrogen and coke production. This damage or contamination of the FCC catalyst can be tracked by testing the circulating inventory of catalyst, as mentioned above. However, periodically poor catalyst performance will be observed with little corresponding explanation in the catalyst properties. This situation can occur from pore blockage of the FCC catalyst caused by particular forms of iron, sodium, calcium or coke and coke precursors (Conradson Carbon Residue) that are present in the feedstock, which deposit on the surface of the catalyst in such a way as to block the catalyst pores without showing significant changes in the bulk metal content in the equilibrium catalyst properties. Correlating the accessibility of porous materials has been disclosed in EP1393045, however, this technique uses probe molecules dissolved in a solvent, where the uptake of the probe molecule from the solvent solution is measured. Thus, it measures a relative “accessibility,” not an actual effective diffusivity of the probe molecule. In addition, gas-phase measurement of diffusion in porous solids is possible by conventional techniques using noble gases as probe molecules. However, these methods do not adequately discriminate among samples for the purpose of diagnosing pore blockage in FCC catalysts because the molecules are much smaller than those encountered commercially, and they do not operate at conditions that adequately simulate those found in operating FCC's.
Thus, there is a need for a process that evaluates the catalytic performance of an FCC catalyst using a vapor diffusion technique. The present disclosure now provides such a method.